Induction of surface exclusion (entry exclusion) by Streptococcus faecalis sex pheromones: Use of monoclonal antibodies to identify an inducible surface antigen involved in the exclusion process

The Streptococcus faecalis plasmid pCF-10 is representative of a class of plasmids that enables its host cells to respond to sex pheromones produced by other S. faecalis cells. The pheromone response has been previously shown to result in increased conjugal plasmid transfer, cell clumping, and multiple cell-surface antigenic changes. To test for other effects of pheromone induction, cells carrying pCF-10 were used as recipients in matings with an isogenic donor strain carrying a derivative of pCF-10, tagged with a transposon to provide an additional selective marker. Pheromone induction of the 'male recipients' decreased their recipient ability by a factor of 10-300 in comparison to uninduced cells or plasmid-free recipients. These results indicate that an entry exclusion (surface exclusion) function, similar to that described in studies of plasmids in Gram-negative bacteria, is induced during the S. faecalis pheromone response process. The exclusion operates only against homologous plasmids. Immunological, biochemical, and genetic experiments using monoclonal antibodies reactive with C130, the predominant protein antigen associated with the pheromone response of cells carrying pCF-10, indicate that this antigen is involved in surface exclusion. The data also support the notion that synthesis of C130 involves a post-translational modification of a precursor of C130 to a final product of higher molecular weight form.